The present invention generally relates to providing packet data service to mobile stations, and particularly relates to providing packet data service in the boundary regions of wireless communication network service areas.
In the context of wireless communication networks, one might fairly view some of the developing changes as evolutionary, and some of them as revolutionary. Evolutionary changes typically build on pre-existing capabilities and protocols, and usually include provisions to ensure backward compatibility. On the other hand, revolutionary changes typically represent a departure from prior practices, and are oftentimes incompatible with the existing standards. These disadvantages usually are offset by performance or efficiency improvements that simply cannot be achieved while preserving backwards compatibility.
Generally, cdma2000 networks include a mix of evolutionary and revolutionary technologies. For example, the older IS-95B networks standard provided low-rate dedicated channels on the forward link supporting circuit-switched voice and data services. For backwards compatibility, cdma2000 network standards preserved these low-rate forward link channels, referred to as Forward Fundamental Channels (F-FCHs). However, these low rate channels may be used for circuit-switched and packet-switched services in cdma2000 networks, albeit limited to typical data rates of 9.6 Kbps.
In a revolutionary break from the pre-existing IS-95B channel definitions, cdma2000 standards defined a new type of dedicated forward link channel, the Forward Supplemental Channel (F-SCH). One or more F-SCHs can be assigned as needed to individual mobile stations to support higher-rate packet data services. F-SCHs can support packet data rates greater than 500 kbps, and have the further advantage of being supported in soft handoff. That is, packet data traffic for F-SCH service to a given mobile station can be sent from the mobile station's source Base Station (BS) to one or more neighboring BSs over the sidehaul links used to communicatively link BSs. The controlling Interoperability Standards (IOSs) define these sidehaul links as the A3/A7 interfaces.
Assuming that a source base station has established a F-SCH with a given mobile station, the F-SCH can be transferred in soft handoff to a neighboring, target base station responsive to the mobile station moving into (or through) a boundary region between the source and target base stations' service areas. To accomplish this, the source base station requests that the target base station setup a F-SCH for the mobile station and, assuming that the request is successful, the source base station begins sending packet data traffic for the mobile station over the A3/A7 sidehaul links for transmission by the target base station on the newly assigned F-SCH.
Since the source base station at least temporarily continues transmitting that packet data on its own F-SCH, the mobile station is served from both the source and target base stations. Of course, if the mobile station moves back toward the source base station, the target base station may tear down its F-SCH. Conversely, if the mobile station moves further away from the source base station, the source base station may tear down its F-SCH, although it continues sending packet data for the mobile station out over the sidehaul links as needed.
As much as F-SCHs have improved achievable packet data service rates in cdma2000 networks, they are not without their drawbacks. For example, F-SCHs are not necessarily efficient in terms of the network resources they utilize. For example, higher F-SCH data rates requires more CDMA spreading code resources—thereby reducing the codes available for other users—and requires potentially significant forward link transmit power—thereby reducing the power available for other users. Newer revisions of the cdma2000 standards address the need for providing efficient higher-rate packet data services by way of defining a new forward link packet data channel type, namely the Forward Packet Data Channel (F-PDCH).
By assigning multiple users to the F-PDCH in a time-sharing arrangement according to a dynamically maintained transmission schedule, one F-PDCH can support high-rate packet data services to a relatively large number of users. That feature obviates the need for allocating dedicated F-SCHs to each user desiring high-rate packet data services. Further, the F-PDCH is transmitted as a rate-controlled channel rather than as a power-controlled channel—F-SCHs in contrast are power-controlled channels.
More particularly, the F-PDCH is transmitted using whatever “leftover” transmit power is available at the RBS after allocating power to the dedicated channels, the broadcast and control channels, and the pilot channel(s). To serve each mobile station at the highest rate supportable given the available F-PDCH transmit power the particular reception conditions prevailing at the mobile station, each mobile station returns Channel Quality Indicator (CQI) reports at a high rate (e.g., 800 Hz). The RBS then sets the individual data rates for transmitting to the individual mobile stations on the F-PDCH based on receiving these CQI reports.
The upshot of this sophistication is that the F-PDCH offers the two-fold advantage of providing typically higher packet data service rates to mobile stations as compared to the rates achievable with dedicated F-SCHs, and offers more efficient utilization of network resources as compared to the use of dedicated F-SCHs. In at least some contexts, however, the F-PDCH suffers from one or more disadvantages.
First, the existing IOSs do not provide for soft handoff of the F-PDCH between different base stations—note the F-PDCH can be handed off between different RBSs operating under control of the same Base Station Controller, assuming the involved RBSs each support the F-PDCH. Second, in a given network, not every RBS will be configured to support the F-PDCH, thus giving rise to different service areas having mixed capabilities. That is, two adjacent service areas may both support F-SCH packet data service, but only one of them supports F-PDCH packet data service.
In the first instance, packet data service on the F-PDCH cannot be continued across the boundary region between source and target base station service areas because the source base station has no defined mechanism for sharing the packet data traffic across its A3/A7 sidehaul links with the target base station. In the second instance, packet data service on the F-PDCH cannot be continued across the boundary region between source and target base station service areas simply because the target base station does not support the F-PDCH. In both instances, the problem of continuing high-rate packet data services to a mobile station moving in, or through, a boundary region is left unaddressed.